This invention relates to the field of data storage, and more particularly to write heads and methods for recording information on data storage media using near-field optical coupling structures.
Magnetic recording heads are used in magnetic disc drive storage systems. Most magnetic recording heads used in such systems today are xe2x80x9clongitudinalxe2x80x9d magnetic recording heads. Longitudinal magnetic recording in its conventional form has been projected to suffer from superparamagnetic instabilities at densities above approximately 40 Gbit/in2. It is believed that reducing or changing the bit cell aspect ratio will extend this limit up to approximately 100 Gbit/in2. However, for recording densities above 100 Gbit/in2, different approaches will likely be necessary to overcome the limitations of longitudinal magnetic recording.
An alternative to longitudinal recording that overcomes at least some of the problems associated with the superparamagnetic effect is xe2x80x9cperpendicularxe2x80x9d magnetic recording. Perpendicular magnetic recording is believed to have the capability of extending recording densities well beyond the limits of longitudinal magnetic recording. Perpendicular magnetic recording heads for use with perpendicular magnetic storage media may include a pair of magnetically coupled poles, including a write pole having a relatively small bottom surface area and a return pole having a larger bottom surface area. A coil having a plurality of turns is located adjacent to the write pole for inducing a magnetic field between the pole and a soft underlayer of the storage media. The soft underlayer is located below a hard magnetic recording layer of the storage media and enhances the amplitude of the field produced by the write pole. In the recording process, an electric current in the coil energizes the write pole, which produces a magnetic field. The image of this field is produced in the soft underlayer to enhance the field strength produced in the magnetic media. Magnetic flux that emerges from the write pole passes into the soft underlayer and returns through the return flux pole. The return pole is located sufficiently far apart from the main write pole such that the material of the return pole does not affect the magnetic flux of the write pole, which is directed vertically into the hard layer of the storage media. This allows the use of storage media with higher coercive force, consequently, more stable bits can be stored in the media.
As the magnetic media grain size is reduced for high areal density recording, superparamagnetic instabilities become an issue. The superparamagnetic effect is most evident when the grain volume V is sufficiently small that the inequality KUV/kBT  greater than 40 can no longer be maintained. Ku is the material""s magnetic crystalline anisotropy energy density, kB is Boltzmann""s constant, and T is absolute temperature. When this inequality is not satisfied, thermal energy demagnetizes the individual grains and the stored data bits will not be stable. Therefore, as the grain size is decreased in order to increase the areal density, a threshold is reached for a given material Ku and temperature T such that stable data storage is no longer feasible.
The thermal stability can be improved by employing a recording medium formed of a material with a very high Ku. However, the available recording heads are not able to provide a sufficient or high enough magnetic writing field to write on such a medium. Heat assisted magnetic recording, sometimes referred to as optical or thermal assisted recording, has been proposed to overcome at least some of the problems associated with the superparamagnetic effect. Heat assisted magnetic recording generally refers to the concept of locally heating a recording medium to reduce the coercivity of the recording medium so that an applied magnetic writing field can more easily direct the magnetization of the recording medium during the temporary magnetic softening of the recording medium caused by the heat source.
By heating the medium, the Ku or the coercivity is reduced such that the magnetic write field is sufficient to write to the medium. Once the medium cools to ambient temperature, the medium has a sufficiently high value of coercivity to assure thermal stability of the recorded information. When applying a heat or light source to the medium, it is desirable to confine the heat or light to the track where writing is taking place and to generate the write field in close proximity to where the medium is heated to accomplish high areal density recording. The separation between the heated spot and the write field spot should be minimal or as small as possible so that writing may occur while the medium temperature is substantially above ambient temperature. This also provides for the efficient cooling of the medium once the writing is completed.
In order to increase areal density in an optically assisted write head, the spot size of the optical beam can be decreased by either decreasing the wavelength of the light or increasing the numerical aperture of the focusing elements. Other optical techniques which either directly or indirectly reduce the effective optical spot size are generally referred to as xe2x80x9csuperresolutionxe2x80x9d techniques. For example, it is well known that the resolving power of a microscope can be increased by placing an aperture with a pinhole (having a diameter smaller than the focused spot size) sufficiently close to the object being observed. As another example, tapered optical fibers have been used to achieve superresolution in near field scanning optical microscopy.
There is identified a need for an improved magnetic recording head that overcomes limitations, disadvantages, and/or shortcomings of known optically assisted magnetic recording heads.
This invention provides a recording head for use in conjunction with a magnetic storage medium, comprising a waveguide for providing a path for transmitting radiant energy; a near-field coupling structure positioned in the waveguide and including a plurality of arms, each having a planar section and a bent section, wherein the planar sections are substantially parallel to a surface of the magnetic storage medium, and the bent sections extend toward the magnetic storage medium and are separated to form a gap adjacent to an air bearing surface; and means for applying a magnetic write field to sections of the magnetic recording medium heated by the radiant energy.
The recording head can further comprise a semi-reflective layer positioned in the path to form a resonant cavity with a surface of the magnetic storage medium. The means for applying a magnetic write field to the magnetic recording medium can comprise a magnetic yoke having a write pole, a return pole, and a coil for producing magnetic flux in the yoke, wherein the near-field coupling structure is position adjacent to the write pole.
The waveguide can comprise a transparent layer mounted adjacent to the write pole, wherein the write pole is located down track from the near-field coupling structure. The near-field coupling structure can form a square opening adjacent to the air bearing surface of the recording head.
The invention also encompasses a magnetic disc drive storage system comprising a housing; means for supporting a magnetic storage medium positioned in the housing; and means for positioning a recording head adjacent to the rotatable magnetic storage medium, wherein the recording head includes a waveguide for providing a path for transmitting radiant energy; a near-field coupling structure positioned in the waveguide and including a plurality of arms, each having a planar section and a bent section, wherein the planar sections are substantially parallel to a surface of the magnetic storage medium, and the bent sections extend toward the magnetic storage medium and are separated to form a gap adjacent to an air bearing surface; and means for applying a magnetic write field to sections of the magnetic recording medium heated by the radiant energy.
The invention further encompasses a method of recording data on a data storage medium, comprising heating a section of the data storage medium by applying radiant energy to a waveguide including a transparent layer, a semi-reflective layer, and a near-field coupling structure at a frequency such that radiant energy resonates between the semi-reflective layer and a surface of the data storage medium; and applying a magnetic write field to the section of data storage medium.